Don't use handles in the Calendar event name migration

Summary:
Fixes T8209. Using handles can now cause cache fills as a side effect of T7707. Use a raw query instead.

I'll follow up on T8209 with some context and ideas for longer-term fixes.

Test Plan:

• Set event names to ''.
• Reran migration with --apply ... --trace.
• Saw migration work correctly without executing cache fills.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8209

Differential Revision: https://secure.phabricator.com/D12858